286 MISCELLANEOUS NITROGEN AND SULFUR COMPOUNDS 



have been extensively cnromatographed by Schultz and coworkers (29, 30) using a butanol- 

 acetic acid-water solvent. The glucosides are recognized by spraying with 0. 02 M silver 

 nitrate, drying at 100° C. and spraying with 0.02 M potassium dichromate. Glucosides 

 appear as yellow spots against a red background of silver chromate. Paper chromato- 

 graphy of the mustard oils is usually carried out using the corresponding thiourea deriva- 

 tives prepared by allowing the f so -thiocyanate to react with concentrated ammonia in 

 ethanol: 



S 



II 

 RNCS + NH3 - R-NHCNHj 



These substituted thioureas also make nicely crystalline derivatives for other character- 

 ization procedures. The thioureas are chromatographed in solvents such as water -satu- 

 rated chloroform or butanol-ethanol-water. One of the most used sprays is Grote's 

 reagent--a mixture of sodium nitroprusside, hydroxylamine and bromine which gives 

 blue spots with thiourea derivatives. This method was developed by Kjaer and Rubinstein 

 (31) and has been used by Kjaer and coworkers in a large number of studies on the mus- 

 tard oils. Similar surveys have been carried out by Delaveau (32) using ammoniacal 

 silver nitrate to detect free iso-thiocyanates. Gas phase chromatography is also useful 

 for volatile members of this group. Spectroscopic evidence is valuable in some cases. 

 The mustard oils show an absorption peak at about 250 m/i. On reaction with ammonia 

 to form a thiourea this changes to about 243 m^i.. Compounds such as goitrin (oxazolidi- 

 nethiones) also show the 243 m/i peak. 



Practically nothing can be said regarding biosynthetic pathways of the mustard oil 

 glycosides. It is evident that the alkyl groups of many of them are similar to the carbon 

 chains of many amino acids less their carboxyl groups. This correspondence suggests 

 a biochemical relationship, but no experiments have been carried out to elucidate it. 



NITRILES 



The nitriles or organic cyanides are widely distributed throughout the plant kingdom, 

 although certain types appear to be taxonomically restricted. The largest single group 

 of natural nitriles is made up of the cyanogenic glycosides whose general structure is as 

 follows: 



0-/-&LYCOSYL 

 I 

 R — C— CN 



I' 



In some cases R' is hydrogen rather than an alkyl group. These compounds possess the 

 general characteristics of other glycosides as colorless compounds soluble in water and 

 to some extent in alcohol but insoluble in fat solvents. They are very common in seeds 

 of the Rosaceae but occur throughout the plant kingdom, including some ferns and fungi. 

 Only a few different aglycones are known, but there are over a dozen different glycosides 

 since the same aglycone may be found with several different sugar components. Like 

 the mustard oil glucosides the cyanogenic glycosides on enzymatic hydrolysis do not nor- 

 mally yield the aglycone as such, but a second reaction occurs to form hydrogen cyanide: 



O-^-G-LYCOSYL OH 



I I II , , 



CCN > RCCN > RCR -I- HCN 



R' R' 



